Cermets are powder metallurgical materials with hard material component and a binding component. Customarily the predominant hard material component consists of a titanium compound, as e.g. of TiN, TiC, Ti(C,N). As binding component it is customary to use Ni, often alloyed with Co. Other elements which are frequently added to cermets are Mo and Ta.
It is customary to use cermet tools without any coating, this in difference to traditional hard metal tools on the basis of WC, which are coated with a refining coating acting as wear resistant coating.
From the EP-A-0 149 024 according to U.S. Pat. No. 4,693,944 it is, nevertheless, known to refine cermet tools with a TiC, TiN, TiCN, TiCO, TiNO or TiCNO coating, from the EP-A-0 269 525 according to U.S. Pat. No. 4,902,395 with a refinement coating of TiC, TiN or TiCN or of a mixture of these materials.
Finally, it is known from the EP-A-0 440 157 to provide on cermet tools a TiN refining layer.
Although the said refining layers, which are used on cermet tools rather seldom, have been said to be wear reducing layers, such an effect of such layers is not generally approved. Therefore, they may not be mentioned as strictly wear resistant coatings. This because by applying such layers only a protection of the cermet binding component against premature wear is reached, but not an improvement of wear characteristics of the cermet hard material component. This is especially true at high temperatures as do occur when such cermet tools, and especially such cermet cutting tools, are used in practice. Such cutting tools of cermets are normally used without cooling emulsion and are typically used for high cutting speed, so e.g. for finishing operations.
The wear resistance of cermet materials could be improved by lowering the content of binding material component. This would lead to reduction of toughness of such cermet material.
With respect to possible compositions of cermet material, attention is drawn to the said three references which shall be integrated part of the present description with respect to examples of possible cermet compositions.